2018 |
Nieuwjaer, N., Desfrancois, C., Lecomte, F., Manil, B., Soorkia, S., Broquier, M., & Gregoire, G. (2018). Photodissociation Spectroscopy of Cold Protonated Synephrine: Surprising Differences between IR-UV Hole-Burning and IR Photodissociation Spectroscopy of the O-H and N-H Modes. J Phys Chem A, .
Résumé: We report the UV and IR photofragmentation spectroscopies of protonated synephrine in a cryogenically cooled Paul trap. Single (UV or IR) and double (UV-UV and IR-UV) resonance spectroscopies have been performed and compared to quantum chemistry calculations, allowing the assignment of the lowest-energy conformer with two rotamers depending on the orientation of the phenol hydroxyl (OH) group. The IR-UV hole burning spectrum exhibits the four expected vibrational modes in the 3 mum region, i.e., the phenol OH, Cbeta-OH, and two NH2(+) stretches. The striking difference is that, among these modes, only the free phenol OH mode is active through IRPD. The protonated amino group acts as a proton donor in the internal hydrogen bond and displays large frequency shifts upon isomerization expected during the multiphoton absorption process, leading to the so-called IRMPD transparency. More interestingly, while the Cbeta-OH is a proton acceptor group with moderate frequency shift for the different conformations, this mode is still inactive through IRPD.
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Noble, J. A., Broquier, M., Gregoire, G., Soorkia, S., Pino, G. A., Marceca, E., Dedonder-Lardeux, C., & Jouvet, C. (2018). Tautomerism and electronic spectroscopy of protonated 1- and 2-aminonaphthalene. Phys. Chem. Chem. Phys., 20, 6134–6145.
Résumé: Experimental and theoretical investigations of the excited states of protonated 1- and 2-aminonaphthalene are presented. The electronic spectra are obtained by laser induced photofragmentation of the ions captured in a cold ion trap. Using ab initio calculations, the electronic spectra can be assigned to different tautomers which have the proton on the amino group or on the naphthalene moiety. It is shown that the tautomer distribution can be varied by changing the electrospray source conditions, favoring either the most stable form in solution (amino protonation) or that in the gas phase (aromatic ring protonation). Calculations for larger amino-polyaromatics predict that these systems should behave as “proton sponges” i.e. have a proton affinity larger than 11 eV.
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Shafizadeh, N., Boyé-Péronne, S., Soorkia, S., Chen, S., de la Lande, A., Cunha de Miranda, B., Garcia, G. A., Nahon, L., Poisson, L., & Soep, B. (2018). The surprisingly high ligation energy of CO to Ruthenium porphyrins. Phys. Chem. Chem. Phys., 20, 11730–11739.
Résumé: A combined theoretical and experimental approach has been used to investigate the binding energy of a ruthenium metalloporphyrin ligated with CO, ruthenium tetraphenylporphyrin [RuII TPP], in the RuII oxidation degree. Measurements performed with VUV ionization using the DESIRS beamline at Synchrotron SOLEIL led to adiabatic ionization energies of [RuII TPP] and its complex with CO, [RuII TPP–CO], of 6.48
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2017 |
Broquier, M., Soorkia, S., Pino, G., Dedonder-Lardeux, C., Jouvet, C., & Gregoire, G. (2017). Excited State Dynamics of Cold Protonated Cytosine Tautomers: Characterization of Charge Transfer, Intersystem Crossing, and Internal Conversion Processes. J. Phys. Chem. A, 121(34), 6429–6439.
Résumé: Charge transfer reactions are ubiquitous in chemical reactivity and often viewed as ultrafast processes. For DNA, femtochemistry has undeniably revealed the primary stage of the deactivation dynamics of the locally excited state following electronic excitation. We here demonstrate that the full time scale excited state dynamics can be followed up to milliseconds through an original pump-probe photodissociation scheme applied to cryogenic ion spectroscopy. Protonated cytosine is chosen as a benchmark system in which the locally excited (1)pipi* state decays in the femtosecond range toward long-lived charge transfer and triplet states with lifetimes ranging from microseconds to milliseconds, respectively. A three-step mechanism ((1)pipi* --> (1)CT --> (3)pipi*) is proposed where internal conversion from each state can occur leading ultimately to fragmentation in the ground electronic state.
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Garcia, R. L., Nieuwjaer, N., Desfrancois, C., Lecomte, F., Leite, S. D., Manil, B., Broquier, M., & Gregoire, G. (2017). Vibronic spectra of protonated hydroxypyridines: contributions of prefulvenic and planar structures. Phys. Chem. Chem. Phys., 19(12), 8258–8268.
Résumé: Various hydroxypyridine derivatives are endogenous or synthetic photosensitizers which could contribute to solar radiation damage. The study of their excited states could lead to a better understanding of their action mechanisms. We present here the ultraviolet (UV) spectra of the protonated 2-, 3- and 4-hydroxypyridine. These spectra were obtained with an experimental device coupling an electrospray ion source with a cold quadrupole ion trap and a time of flight mass spectrometer. They display well resolved vibrational structures, with a clear influence of the position of the OH group. These results are interpreted with excited states calculations at the coupled cluster CC2 level.
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2016 |
Broquier, M., Soorkia, S., Dedonder-Lardeux, C., Jouvet, C., Theule, P., & Gregoire, G. (2016). Twisted Intramolecular Charge Transfer in Protonated Amino Pyridine. J. Phys. Chem. A, 120(21), 3797–3809.
Résumé: The excited state properties of protonated ortho (2-), meta (3-), and para (4-) aminopyridine molecules have been investigated through UV photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Cryogenic ion spectroscopy allows recording well-resolved vibronic spectroscopy that can be reproduced through Franck-Condon simulations of the pipi* local minimum of the excited state potential energy surface. The excited state lifetimes have also been measured through a pump-probe excitation scheme and compared to the estimated radiative lifetimes. Although protonated aminopyridines are rather simple aromatic molecules, their deactivation mechanisms are indeed quite complex with unexpected results. In protonated 3- and 4-aminopyridine, the fragmentation yield is negligible around the band origin, which implies the absence of internal conversion to the ground state. Besides, a twisted intramolecular charge transfer reaction is evidenced in protonated 4-aminopyridine around the band origin, while excited state proton transfer from the pyridinic nitrogen to the adjacent carbon atom opens with roughly 500 cm-1 of excess energy.
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Pino, G. A., Feraud, G., Broquier, M., Gregoire, G., Soorkia, S., Dedonder, C., & Jouvet, C. (2016). Non-radiative processes in protonated diazines, pyrimidine bases and an aromatic azine. Phys. Chem. Chem. Phys., 18(30), 20126–20134.
Résumé: The excited state lifetimes of DNA bases are often very short due to very efficient non-radiative processes assigned to the pipi*-npi* coupling. A set of protonated aromatic diazine molecules (pyridazine, pyrimidine and pyrazine C4H5N2+) and protonated pyrimidine DNA bases (cytosine, uracil and thymine), as well as the protonated pyridine (C5H6N+), have been investigated. For all these molecules except one tautomer of protonated uracil (enol-keto), electronic spectroscopy exhibits vibrational line broadening. Excited state geometry optimization at the CC2 level has been conducted to find out whether the excited state lifetimes measured from line broadening can be correlated to the calculated ordering of the pipi* and npi* states and the pipi*-npi* energy gap. The short lifetimes, observed when one nitrogen atom of the ring is not protonated, can be rationalized by relaxation of the pipi* state to the npi* state or directly to the electronic ground state through ring puckering.
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Soorkia, S., Broquier, M., & Gregoire, G. (2016). Multiscale excited state lifetimes of protonated dimethyl aminopyridines. Phys. Chem. Chem. Phys., 18(34), 23785–23794.
Résumé: The excited state dynamics of protonated ortho (2-) and para (4-) dimethyl aminopyridine molecules (DMAPH(+)) has been studied through pump-probe photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Multiscale temporal dynamics has been recorded over 9 orders of magnitude from subpicosecond to millisecond. The initially locally excited pipi* state rapidly decays within about 100 fs into a charge transfer state following 90 degrees twist motion of the dimethyl amino group. While this twisted intramolecular charge transfer (TICT) state does not trigger any fragmentation, it selectively leads to specific two-color photofragments through absorption of the probe photon at 355 nm. Besides, the optically dark TICT state provides an efficient deactivation path with high intersystem probability to non-dissociative long-lived triplet states. Such a multiscale pump-probe photodissociation scheme paves the way to systematic studies of charge transfer reactions in the excited state of cold ionic systems stored in a cryogenic cooled ion trap and probed continuously up to the millisecond time scale.
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2015 |
Broquier, M., Soorkia, S., & Gregoire, G. (2015). A comprehensive study of cold protonated tyramine: UV photodissociation experiments and ab initio calculations. Phys Chem Chem Phys, 17, 25854–25862.
Résumé: We present a comprehensive experimental study of protonated tyramine ions in a cold 3D quadrupole ion trap coupled to a time-of-flight mass spectrometer. Multiple UV photodissociation techniques have been developed, including single and double resonance spectroscopy along with time-resolved excited state lifetime measurements through a picosecond pump-probe scheme. An original UV-UV hole burning method is presented which can be used without modification of the quadrupole ion trap. The electronic spectrum of the cold protonated tyramine exhibits well-defined vibronic transitions, allowing the firm assignment of its two low-lying energy conformations by comparison with CC2 ab initio excited state calculations.
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Feraud, G., Broquier, M., Dedonder, C., Jouvet, C., Gregoire, G., & Soorkia, S. (2015). Excited State Dynamics of Protonated Phenylalanine and Tyrosine: Photo-Induced Reactions Following Electronic Excitation. J Phys Chem A, 119(23), 5914–5924.
Résumé: The electronic spectroscopy and the electronic excited state properties of cold protonated phenylalanine and protonated tyrosine have been revisited on a large spectral domain and interpreted by comparison with ab initio calculations. The protonated species are stored in a cryogenically cooled Paul trap, maintained at approximately 10 K, and the parent and all the photofragment ions are mass-analyzed in a time-of-flight mass spectrometer, which allows detecting the ionic species with an improved mass resolution compared to what is routinely achieved with a quadrupole mass spectrometer. These new results emphasize the competition around the band origin between two proton transfer reactions from the ammonium group toward either the aromatic chromophore or the carboxylic acid group. These reactions are initiated by the coupling of the locally excited pipi* state with higher charge transfer states, the positions and coupling of which depend on the conformation of the protonated molecules. Each of these reaction processes gives rise to specific fragmentation channels that supports the conformer selectivity observed in the photofragmentation spectra of protonated tyrosine and phenylalanine.
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Ferrand, L., Soorkia, S., Gregoire, G., Broquier, M., Soep, B., & Shafizadeh, N. (2015). Bonding of heme FeIIIwith dioxygen: Observation and characterization of an incipient bond. Phys. Chem. Chem. Phys., 17, 25693–25699.
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Hernandez, F. J., Capello, M. C., Naito, A., Manita, S., Tsukada, K., Miyazaki, M., Fujii, M., Broquier, M., Gregoire, G., Dedonder-Lardeux, C., Jouvet, C., & Pino, G. A. (2015). Trapped Hydronium Radical Produced by Ultraviolet Excitation of Substituted Aromatic Molecule. J Phys Chem A, 119(51), 12730–12735.
Résumé: The gas phase structure and excited state dynamics of o-aminophenol-H2O complex have been investigated using REMPI, IR-UV hole-burning spectroscopy, and pump-probe experiments with picoseconds laser pulses. The IR-UV spectroscopy indicates that the isomer responsible for the excitation spectrum corresponds to an orientation of the OH bond away from the NH2 group. The water molecule acts as H-bond acceptor of the OH group of the chromophore. The complexation of o-aminophenol with one water molecule induced an enhancement in the excited state lifetime on the band origin. The variation of the excited state lifetime of the complex with the excess energy from 1.4 +/- 0.1 ns for the 0-0 band to 0.24 +/- 0.3 ns for the band at 0-0 + 120 cm(-1) is very similar to the variation observed in the phenol-NH3 system. This experimental result suggests that the excited state hydrogen transfer reaction is the dominant channel for the non radiative pathway. Indeed, excited state ab initio calculations demonstrate that H transfer leading to the formation of the H3O(*) radical within the complex is the main reactive pathway.
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Soorkia, S., Dehon, C., S, S. K., Perot-Taillandier, M., Lucas, B., Jouvet, C., Barat, M., & Fayeton, J. A. (2015). Ion-Induced Dipole Interactions and Fragmentation Times: Calpha-Cbeta Chromophore Bond Dissociation Channel. J Phys Chem Lett, 6(11), 2070–2074.
Résumé: The fragmentation times corresponding to the loss of the chromophore (Calpha-Cbeta bond dissociation channel) after photoexcitation at 263 nm have been investigated for several small peptides containing tryptophan or tyrosine. For tryptophan-containing peptides, the aromatic chromophore is lost as an ionic fragment (m/z 130), and the fragmentation time increases with the mass of the neutral fragment. In contrast, for tyrosine-containing peptides the aromatic chromophore is always lost as a neutral fragment (mass = 107 amu) and the fragmentation time is found to be fast (<20 ns). These different behaviors are explained by the role of the postfragmentation interaction in the complex formed after the Calpha-Cbeta bond cleavage.
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2014 |
Feraud, G., Broquier, M., Dedonder-Lardeux, C., Gregoire, G., Soorkia, S., & Jouvet, C. (2014). Photofragmentation spectroscopy of cold protonated aromatic amines in the gas phase. Phys Chem Chem Phys, 16(11), 5250–5259.
Résumé: The electronic spectra of cold protonated aromatic amines: anilineH(+) C6H5-NH3(+), benzylamineH(+) C6H5-CH2-NH3(+) and phenylethylamineH(+) C6H5-(CH2)2-NH3(+) have been investigated experimentally in a large spectral domain and are compared to those of their hydroxyl homologues. In the low energy region, the electronic spectra are similar to their neutral analogues, which reveals the pipi* character of their first excited state. A second transition is observed from 0.4 to 1 eV above the origin band, which is assigned to the excitation of the pisigma* state. In these protonated amine molecules, there is a competition between different fragmentation channels, some being specific to UV excitation i.e., not observed in low-energy collision induced dissociation experiments. Besides, for one amine a drastic change in the fragmentation branching ratio is observed within a very short energy range that reveals the complex excited state dynamics and fragmentation processes. The experimental observations can be rationalized using a simple qualitative model, the pipi*-pisigma* model [A. L. Sobolewski, W. Domcke, C. Dedonder-Lardeux and C. Jouvet, Phys. Chem. Chem. Phys., 2002, 4, 1093-1100], which predicts that the excited state dynamics is controlled by the crossing between the pipi* excited state and a pisigma* state repulsive along the XH (X being O or N) coordinate.
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Feraud, G., Dedonder-Lardeux, C., Soorkia, S., & Jouvet, C. (2014). Photo-fragmentation spectroscopy of benzylium and 1-phenylethyl cations. J Chem Phys, 140(2), 024302.
Résumé: The electronic spectra of cold benzylium (C6H5-CH2 (+)) and 1-phenylethyl (C6H5-CH-CH3 (+)) cations have been recorded via photofragment spectroscopy. Benzylium and 1-phenylethyl cations produced from electrosprayed benzylamine and phenylethylamine solutions, respectively, were stored in a cryogenically cooled quadrupole ion trap and photodissociated by an OPO laser, scanned in parts of the UV and visible regions (600-225 nm). The electronic states and active vibrational modes of the benzylium and 1-phenylethyl cations as well as those of their tropylium or methyl tropylium isomers have been calculated with ab initio methods for comparison with the spectra observed. Sharp vibrational progressions are observed in the visible region while the absorption features are much broader in the UV. The visible spectrum of the benzylium cation is similar to that obtained in an argon tagging experiment [V. Dryza, N. Chalyavi, J. A. Sanelli, and E. J. Bieske, J. Chem. Phys. 137, 204304 (2012)], with an additional splitting assigned to Fermi resonances. The visible spectrum of the 1-phenylethyl cation also shows vibrational progressions. For both cations, the second electronic transition is observed in the UV, around 33,000 cm(-1) (4.1 eV) and shows a broadened vibrational progression. In both cases the S2 optimized geometry is non-planar. The third electronic transition observed around 40,000 cm(-1) (5.0 eV) is even broader with no apparent vibrational structures, which is indicative of either a fast non-radiative process or a very large change in geometry between the excited and the ground states. The oscillator strengths calculated for tropylium and methyl tropylium are weak. Therefore, these isomeric structures are most likely not responsible for these absorption features. Finally, the fragmentation pattern changes in the second and third electronic states: C2H2 loss becomes predominant at higher excitation energies, for both cations.
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Soorkia, S., Broquier, M., & Grégoire, G. (2014). Conformer- and Mode-Specific Excited State Lifetimes of Cold Protonated Tyrosine Ions. J. Phys. Chem. Lett., 5(24), 4349–4355.
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Soorkia, S., Dehon, C., Kumar, S. S., Pedrazzani, M., Frantzen, E., Lucas, B., Barat, M., Fayeton, J. A., & Jouvet, C. (2014). UV Photofragmentation Dynamics of Protonated Cystine: Disulfide Bond Rupture. J Phys Chem Lett, 5(7), 1110–1116.
Résumé: Disulfide bonds (S-S) play a central role in stabilizing the native structure of proteins against denaturation. Experimentally, identification of these linkages in peptide and protein structure characterization remains challenging. UV photodissociation (UVPD) can be a valuable tool in identifying disulfide linkages. Here, the S-S bond acts as a UV chromophore and absorption of one UV photon corresponds to a sigma-sigma* transition. We have investigated the photodissociation dynamics of protonated cystine, which is a dimer of two cysteines linked by a disulfide bridge, at 263 nm (4.7 eV) using a multicoincidence technique in which fragments coming from the same fragmentation event are detected. Two types of bond cleavages are observed corresponding to the disulfide (S-S) and adjacent C-S bond ruptures. We show that the S-S cleavage leads to three different fragment ions via three different fragmentation mechanisms. The UVPD results are compared to collision-induced dissociation (CID) and electron-induced dissociation (EID) studies.
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2013 |
Capello, M. C., Broquier, M., Dedonder-Lardeux, C., Jouvet, C., & Pino, G. A. (2013). Fast excited state dynamics in the isolated 7-azaindole-phenol H-bonded complex. J Chem Phys, 138(5), 054304.
Résumé: The excited state dynamics of the H-bonded 7-azaindole-phenol complex (7AI-PhOH) has been studied by combination of picosecond pump and probe experiments, LIF measurements on the nanosecond time scale and ab initio calculations. A very short S(1) excited state lifetime (30 ps) has been measured for the complex upon excitation of the 0(0)(0) transition and the lifetime remains unchanged when the nu(6) vibrational mode (0(0)(0) + 127 cm(-1)) is excited. In addition, no UV-visible fluorescence was observed by exciting the complex with nanosecond pulses. Two possible deactivation channels have been investigated by ab initio calculations: first an excited state tautomerization assisted by a concerted double proton transfer (CDPT) and second an excited state concerted proton electron transfer (CPET) that leads to the formation of a radical pair (hydrogenated 7AIH() radical and phenoxy PhO() radical). Both channels, CDPT and CPET, seem to be opened according to the ab initio calculations. However, the analysis of the ensemble of experimental and theoretical evidence indicates that the excited state tautomerization assisted by CDPT is quite unlikely to be responsible for the fast S(1) state deactivation. In contrast, the CPET mechanism is suggested to be the non-radiative process deactivating the S(1) state of the complex. In this mechanism, the lengthening of the OH distance of the PhOH molecule induces an electron transfer from PhOH to 7AI that is followed by a proton transfer in the same kinetic step. This process leads to the formation of the radical pair (7AIH()...PhO()) in the electronically excited state through a very low barrier or to the ion pair (7AIH(+)...PhO(-)) in the ground state. Moreover, it should be noted that, according to the calculations the pisigma* state, which is responsible for the H loss in the free PhOH molecule, does not seem to be involved at all in the quenching process of the 7AI-PhOH complex.
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Dehon, C., Soorkia, S., Pedrazzani, M., Jouvet, C., Barat, M., Fayeton, J. A., & Lucas, B. (2013). Photofragmentation at 263 nm of small peptides containing tyrosine: role of the charge transfer on CO. Phys. Chem. Chem. Phys., 15, 8779–8788.
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Miyazaki, M., Kawanishi, A., Nielsen, I., Alata, I., Ishiuchi, S. -ichi, Dedonder, C., Jouvet, C., & Fujii, M. (2013). Ground state proton transfer in phenol-(NH3)(n) (n </= 11) clusters studied by mid-IR spectroscopy in 3-10 mum range. J Phys Chem A, 117(7), 1522–1530.
Résumé: The infrared (IR) spectra of size-selected phenol-ammonia clusters, PhOH-(NH(3))(n) (n </= 11) in the 3-10 mum wavelength region were measured to investigate the critical number of solvent molecules necessary to promote the ground state proton transfer (GSPT) reaction. While the N-H stretching vibrations did not provide clear information, characteristic changes that are assigned to the GSPT reaction were observed in the skeletal vibrational region. The production of phenolate anion (PhO(-)), which is a product of the GSPT reaction, was established from the appearance of characteristic bands assignable to C-C stretching and C-H bending vibrations of PhO(-) and from the corresponding disappearance of C-O-H bending vibration of PhOH at n = 9. The mid-IR spectroscopy directly proves the structural change induced by the deprotonation from the O-H bond and thus establishes the GSPT reaction as complete at n = 9. No such absorptions were observed for n </= 5 in line with a previous report. For n = 6-8, both the proton transferred and the nontransferred signatures were observed in the spectra, showing coexistence of both species for the first time.
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2012 |
Malis, M., Loquais, Y., Gloaguen, E., Biswal, H. S., Piuzzi, F., Tardivel, B., Brenner, V., Broquier, M., Jouvet, C., Mons, M., Doslic, N., & Ljubic, I. (2012). Unraveling the mechanisms of nonradiative deactivation in model peptides following photoexcitation of a phenylalanine residue. J Am Chem Soc, 134(50), 20340–20351.
Résumé: The mechanisms of nonradiative deactivation of a phenylalanine residue after near-UV photoexcitation have been investigated in an isolated peptide chain model (N-acetylphenylalaninylamide, NAPA) both experimentally and theoretically. Lifetime measurements at the origin of the first pipi* state of jet-cooled NAPA molecules have shown that (i) among the three most stable conformers of the molecule, the folded conformer NAPA B is approximately 50-times shorter lived than the extended major conformer NAPA A and (ii) this lifetime is virtually insensitive to deuteration at the NH(2) and NH sites. Concurrent time-dependent density functional theory (TDDFT) based nonadiabatic dynamics simulations in the full dimensionality, carried out for the NAPA B conformer, provided direct insights on novel classes of ultrafast deactivation mechanisms, proceeding through several conical intersections and leading in fine to the ground state. These mechanisms are found to be triggered either (i) by a stretch of the N(Phe)H bond, which leads to an H-transfer to the ring, or (ii) by specific backbone amide distortions. The potential energy surfaces of the NAPA conformers along these critical pathways have been characterized more accurately using the coupled cluster doubles (CC2) method and shown to exhibit barriers that can be overcome with moderate excess energies. These results analyzed in the light of the experimental findings enabled us to assign the short lifetime of NAPA B conformer to a number of easily accessible exit channels from the initial pipi* surface, most importantly the one involving a transfer of electronic excitation to an npi* surface, induced by distortions of the backbone peptide bond.
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Sunil Kumar, S., Lucas, B., Soorkia, S., Barat, M., & Fayeton, J. A. (2012). Calpha-Cbeta chromophore bond dissociation in protonated tyrosine-methionine, methionine-tyrosine, tryptophan-methionine, methionine-tryptophan and their sulfoxide analogs. Phys. Chem. Chem. Phys., 14(29), 10225–32.
Résumé: C(alpha)-C(beta) chromophore bond dissociation in some selected methionine-containing dipeptides induced by UV photons is investigated. In methionine containing dipeptides with tryptophan as the UV chromophore, the tryptophan side chain is ejected either as an ion or as a neutral fragment while in dipeptides with tyrosine, the tyrosine side chain is lost only as a neutral fragment. Mechanisms responsible for these fragmentations are proposed based on measured branching ratios and fragmentation times, and on the results of DFT/B3-LYP calculations. It appears that the C(alpha)-C(beta) bond cleavage is a non-statistical dissociation for the peptides containing tyrosine, and occurs after internal conversion for those with tryptophan. The proposed mechanisms are governed by the ionization potential of the aromatic side chain compared to that of the rest of the molecule, and by the proton affinity of the aromatic side chain compared to that of the methionine side chain. In tyrosine-containing peptides, the presence of oxygen on sulfur of methionine presumably reduces the ionization potential of the peptide backbone, facilitating the loss of the side chain as a neutral fragment. In tryptophan-containing peptides, the presence of oxygen on methionyl-sulfur expedites the transfer of the proton from the side chain to the sulfoxide, which facilitates the loss of the neutral side chain.
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2011 |
Cheong, N. R., Nam, S. H., Park, H. S., Ryu, S., Song, J. K., Park, S. M., Perot, M., Lucas, B., Barat, M., Fayeton, J. A., & Jouvet, C. (2011). Photofragmentation in selected tautomers of protonated adenine. Phys Chem Chem Phys, 13(1), 291–295.
Résumé: The photofragmentation by UV excitation of selectively prepared 1(+) and 3(+) tautomers of protonated adenine is studied after excitation at a 266 and 263 nm wavelengths with two different experimental set-ups located in Seoul and Orsay. While the production of 1(+) tautomers with an electrospray ion source is now well accepted, calculations were used to ascribe the preparation of 3(+) tautomers from cold adenine dimers. The fragmentation patterns are rather similar for both tautomers, suggesting similar mechanisms as a statistical fragmentation in the ground electronic state after internal conversion.
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Kumar, S. S., Perot-Taillandier, M., Lucas, B., Soorkia, S., Barat, M., & Fayeton, J. A. (2011). UV Photodissociation Dynamics of Deprotonated 2 '-Deoxyadenosine 5 '-Monophosphate [5 '-dAMP-H](-). JOURNAL OF PHYSICAL CHEMISTRY A, 115(38), 10383–10390.
Résumé: The UV photodissociation dynamics of deprotonated 2'-deoxyadenosine 5'-monophosphate ([5'-dAMP-H](-)) has been studied using a unique technique based on the coincident detection of the ion and the neutral fragments. The observed fragment ions are m/z 79 (PO3-), 97 (H2PO4-), 134 ([A-H](-)), 177 ([dAMP-H-A-H2O](-)), and 195 ([dAMP-H-A](-)), where “A” refers to a neutral adenine molecule. The relative abundances are comparable to that found in previous studies on [5'-dAMP-H](-) employing different excitation processes, i.e., collisions and UV photons. The fragmentation times of the major channels have been measured, and are all found to be on the microsecond time scale. The fragmentation mechanisms for all channels have been characterized using velocity correlation plots of the ion and neutral fragment(s). The findings show that none of the dissociation channels of [5'-dAMP-H](-) is UV specific and all proceed via statistical fragmentation on the ground state after internal conversion, a result similar to fragmentations induced by collisions.
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2010 |
Perot, M., Lucas, B., Barat, M., Fayeton, J. A., & Jouvet, C. (2010). Mechanisms of UV photodissociation of small protonated peptides. J Phys Chem A, 114(9), 3147–3156.
Résumé: Photofragmentation of protonated dipeptides by 263 nm photons is investigated with an experimental technique based on the detection in coincidence of the ionic and neutral fragments. With this method, it is possible to determine whether the fragmentation takes place in one or several steps. The timing of these steps can also be evaluated. The interpretation of the various fragmentation pathways is tentatively developed along the same line as that previously proposed for tryptophan. The fragmentation can be explained by two types of mechanisms: internal conversions and direct fragmentations triggered by the migration of the photoactive electron on positive charged sites or on oxygen sites.
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2009 |
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Grégoire, G., Lucas, B., Barat, M., Fayeton, J. A., Dedonder-Lardeux, C., & Jouvet, C. (2009). UV photoinduced dynamics in protonated aromatic amino acid. Eur. Phys. J. D, 51(1), 109–116.
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Kadhane, U., Pérot, M., Lucas, B., Barat, M., Fayeton, J. A., Jouvet, C., Ehlerding, A., Kirketerp, M. - B. S., Nielsen, S. B., Wyer, J. A., & Zettergren, H. (2009). Photodissociation of protonated tryptamine and its supramolecular complex with 18-crown-6 ether: Dissociation times and channels, absorption spectra, and excited states calculations. Chemical Physics Letters, 480(1-3), 57–61.
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Lepere, V., Picard, Y. J., Barat, M., Fayeton, J. A., Lucas, B., & Beroff, K. (2009). Photodissociation dynamics of Ar2(+) and Ar3(+) excited by 527 nm photons. J Chem Phys, 130(19), 194301.
Résumé: The photofragmentation dynamics of Ar(2)(+) and Ar(3)(+) clusters has been investigated at a 527 nm wavelength (2.35 eV) using a setup that allows simultaneous detection of the ionic and neutral fragments in a coincidence experiment. Measurement of positions and times of flight enables in principle a complete description of the fragmentation dynamics. The photofragmentation dynamics of Ar(3)(+) clusters is similar to that of Ar(2)(+) with, in addition, the ejection of a third fragment that can be neutral or ionized via a resonant electron capture. This is attributed to the triangular geometry of the Ar(3)(+) ion.
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2008 |
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Lucas, B., Barat, M., Fayeton, J. A., Jouvet, C., Çarçabal, P., & Grégoire, G. (2008). Statistical versus non-statistical photo-fragmentation of protonated GWG tri-peptide induced by UV excitation. Chemical Physics, 347(1-3), 324–330.
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Lucas, B., Barat, M., Fayeton, J. A., Perot, M., Jouvet, C., Gregoire, G., & Brondsted Nielsen, S. (2008). Mechanisms of photoinduced Calpha[Single Bond]Cbeta bond breakage in protonated aromatic amino acids. J Chem Phys, 128(16), 164302.
Résumé: Photoexcitation of protonated aromatic amino acids leads to C(alpha)[Single Bond]C(beta) bond breakage among other channels. There are two pathways for the C(alpha)[Single Bond]C(beta) bond breakage, one is a slow process (microseconds) that occurs after hydrogen loss from the electronically excited ion, whereas the other is a fast process (nanoseconds). In this paper, a comparative study of the fragmentation of four molecules shows that the presence of the carboxylic acid group is necessary for this fast fragmentation channel to occur. We suggest a mechanism based on light-induced electron transfer from the aromatic ring to the carboxylic acid, followed by a fast internal proton transfer from the ammonium group to the negatively charged carboxylic acid group. The ion formed is a biradical since the aromatic ring is ionized and the carbon of the COOH group has an unpaired electron. Breakage of the weak C(alpha)[Single Bond]C(beta) bond gives two even-electron fragments and is expected to quickly occur. The present experimental results together with the ab initio calculations support the interpretation previously proposed.
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2007 |
Gregoire, G., Dedonder-Lardeux, C., Jouvet, C., Desfrancois, C., & Fayeton, J. A. (2007). Ultrafast excited state dynamics in protonated GWG and GYG tripeptides. Phys Chem Chem Phys, 9(1), 78–82.
Résumé: The excited state dynamics of two protonated tripeptides GWG and GYG has been investigated by pump/probe femtosecond measurements on photofragments, to explore the behavior of peptides where the terminal protonated amino group is not directly linked to the aromatic residue. The dynamics observed are short and surprisingly similar to the dynamics observed on the free protonated tryptophan and tyrosine aromatic amino acids. Specific photofragments observed for protonated GWG are related to the formation of a radical species WG degrees (+) after cleavage of the C(alpha)-N bond near the tryptophan residue.
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Gregoire, G., Jouvet, C., Dedonder, C., & Sobolewski, A. L. (2007). Ab initio study of the excited-state deactivation pathways of protonated tryptophan and tyrosine. J Am Chem Soc, 129(19), 6223–6231.
Résumé: In recent experiments, the excited-state lifetimes of protonated aromatic amino acids (TrpH+ and TyrH+) have been recorded by means of pump-probe photodissociation technique. The lifetime of TyrH+ is much longer than that of TrpH+, which has been initially rationalized on the basis of a simple phenomenological model. Besides, specific photofragments including the formation of radical cation after hydrogen loss are observed for TrpH+ that are not found for TyrH+. The ab initio calculations reported here for TrpH+ and TyrH+ using a coupled-cluster method are meant to track the rich photochemistry of these protonated amino acids following UV excitation.
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Lepere, V., Lucas, B., Barat, M., Fayeton, J. A., Picard, V. J., Jouvet, C., Carcabal, P., Nielsen, I., Dedonder-Lardeux, C., Gregoire, G., & Fujii, A. (2007). Comprehensive characterization of the photodissociation pathways of protonated tryptophan. J Chem Phys, 127(13), 134313.
Résumé: The photofragmentation of protonated tryptophan has been investigated in a unique experimental setup, in which ion and neutral issued from the photofragmentation are detected in coincidence, in time and in position. From these data are extracted the kinetic energy, the number of neutral fragments associated with an ion, their masses, and the order of the fragmentation steps. Moreover, the fragmentation time scale ranging from tens of nanoseconds to milliseconds is obtained. From all these data, a comprehensive fragmentation mechanism is proposed.
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Lepere, V., Lucas, B., Barat, M., Fayeton, J. A., Picard, Y. J., Jouvet, C., Carcabal, P., Nielsen, I., Dedonder-Lardeux, C., Gregoire, G., & Fujii, A. (2007). Characterization of neutral fragments issued from the photodissociation of protonated tryptophane. Phys Chem Chem Phys, 9(39), 5330–5334.
Résumé: New information on the photo-fragmentation of biomolecules is obtained from the detection of neutral and ionic fragments using a time and position resolved coincidence technique that reveals whether an ionic photofragment is associated with one or more neutral fragments. In the case of a sequential dissociation, both fragmentation channels are identified as well as their time ordering.
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2006 |
Antoine, R., Broyer, M., Chamot-Rooke, J., Dedonder, C., Desfrancois, C., Dugourd, P., Gregoire, G., Jouvet, C., Onidas, D., Poulain, P., Tabarin, T., & van der Rest, G. (2006). Comparison of the fragmentation pattern induced by collisions, laser excitation and electron capture. Influence of the initial excitation. Rapid Commun Mass Spectrom, 20(11), 1648–1652.
Résumé: Collision-induced dissociation, laser-induced dissociation and electron-capture dissociation are compared on a singly and doubly protonated pentapeptide. The dissociation spectrum depends on the excitation mechanism and on the charge state of the peptide. The comparison of these results with the conformations obtained from Monte Carlo simulations suggests that the de-excitation mechanism following a laser or an electron-capture excitation is related to the initial geometry of the peptide.
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Grégoire, G., Jouvet, C., Dedonder, C., & Sobolewski, A. L. (2006). On the role of dissociative πσ* states in the photochemistry of protonated tryptamine and tryptophan: An ab initio study. Chemical Physics, 324(2-3), 398–404.
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Gregoire, G., Kang, H., Dedonder-Lardeux, C., Jouvet, C., Desfrancois, C., Onidas, D., Lepere, V., & Fayeton, J. A. (2006). Statistical vs. non-statistical deactivation pathways in the UV photo-fragmentation of protonated tryptophan-leucine dipeptide. Phys Chem Chem Phys, 8(1), 122–128.
Résumé: The excited state dynamics of protonated tryptophan-leucine ions WLH+, generated in an electrospray source, is investigated by photo-induced fragmentation in the gas phase, using femtosecond laser pulses. Two main features arise from the experiment. Firstly, the initially excited pipi* state decays very quickly with 2 time constants of 1 and 10 ps. Secondly, the transient signals recorded on different fragments are not the same which indicates two competing primary fragmentation processes. One involves a direct dissociation from the excited state that gives evidence for a non-statistical deactivation path. The other is attributed to a statistical decay following internal conversion to the ground electronic surface.
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2005 |
Kang, H., Dedonder-Lardeux, C., Jouvet, C., Gregoire, G., Desfrancois, C., Schermann, J. - P., Barat, M., & Fayeton, J. A. (2005). Control of bond-cleaving reactions of free protonated tryptophan ion by femtosecond laser pulses. J Phys Chem A, 109(11), 2417–2420.
Résumé: The excited-state dynamics of protonated tryptophan ions is investigated by photoinduced fragmentation in the gas phase. In contrast to the neutral molecule that decays on the nanosecond time scale, the protonated species exhibits an ultrafast decay with two time constants of about 400 fs and 15 ps. In addition, after UV excitation by a pump photon at 266 nm, specific photofragments, and in particular the NH3-loss channel, can be enhanced by the absorption of a probe photon at 800 nm. The bond-cleaving reactions can thus be controlled by a variation of the pump/probe delay.
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Kang, H., Jouvet, C., Dedonder-Lardeux, C., Martrenchard, S., Charriere, C., Gregoire, G., Desfrancois, C., Schermann, J. P., Barat, M., & Fayeton, J. A. (2005). Photoinduced processes in protonated tryptamine. J Chem Phys, 122(8), 84307.
Résumé: The electronic excited state dynamics of protonated tryptamine ions generated by an electrospray source have been studied by means of photoinduced dissociation technique on the femtosecond time scale. The result is that the initially excited state decays very quickly within 250 fs. The photoinduced dissociation channels observed can be sorted in two groups of fragments coming from two competing primary processes on the singlet electronic surface. The first one corresponds to a hydrogen-atom loss channel that creates a tryptamine radical cation. The radical cation subsequently fragments to smaller ions. The second process is internal conversion due to the H-atom recombination on the electronic ground state. Time-dependent density functional theory calculations show that an excited pisigma* state dissociative along the protonated amino N-H stretch crosses both the locally excited pipi* state and the electronic ground state S(0) and thus triggers the photofragmentation reactions. The two processes have equivalent quantum yields, approximately equal to 50% of the fragments coming from the H-atom loss reaction. The two primary reaction paths can clearly be distinguished by their femtosecond pump/probe dynamics recorded on the different fragmentation channels.
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Kang, H., Jouvet, C., Dedonder-Lardeux, C., Martrenchard, S., Grégoire, G., Desfrançois, C., Schermann, J. - P., Barat, M., & Fayeton, J. A. (2005). Ultrafast deactivation mechanisms of protonated aromatic amino acids following UV excitation. Phys. Chem. Chem. Phys., 7(2), 394–398.
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Lepere, V., Ismail, I. M., Barat, M., Fayeton, J. A., Picard, Y. J., Wohrer, K., Jouvet, C., & Martrenchard, S. (2005). Lifetime and yield of metastable Ar2(+) ions. J Chem Phys, 123(17), 174307.
Résumé: Ar2(+) ions produced in a cooled supersonic expansion by electron-impact ionization are accelerated at 2.5 keV and kept during few milliseconds inside a linear electrostatic trap. The lifetime of the metastable Ar2(+) ion is determined from the measurement of the rate of the argon atoms escaping the trap. The lifetime and the relative metastable populations are measured as a function of the pressure and temperature in the supersonic expansion, i.e., of the mean cluster size. Possible mechanisms responsible for the metastable formation are discussed.
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2004 |
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Kang, H., Dedonder-Lardeux, C., Jouvet, C., Martrenchard, S., Grégoire, G., Desfrançois, C., Schermann, J. - P., Barat, M., & Fayeton, J. A. (2004). Photo-induced dissociation of protonated tryptophan TrpH+: A direct dissociation channel in the excited states controls the hydrogen atom loss. Phys. Chem. Chem. Phys., 6(10), 2628–2632.
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